The hypothesis has been developed that at least some of the late slow components of the electroretinogram (ERG) are electrogenic consequences of sodium-dependent active glucose transport across the pigment epithelium. The experimental testing of this hypothesis involves both in vitro and in vivo studies. The in vitro studies are designed to (a) measure the transport and accumulation of ratioactively labeled glucose by the isolated, mammalian pigment epithelium and (b) establish the ionic dependence of the active glucose transport. The in vivo studies will (a) correlate the amplitude and time course of the slow ERG components with the plasma concentration of glucose and (b) determine the effects of glucose transport inhibitors on the slow ERG components. These in vivo studies will be performed while monitoring blood pressure, PO2, PCO2, PH and osmolarity of the blood.